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Liquid Scintillation counting of H-3 and C-14
Evgeny TaskaevEckert & Ziegler Analytics
20th Annual RETS-REMP Workshop San Jose, California, June 28-30, 2010
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H-3Emax = 18.6 keVT1/2 = 12.43 y1TU(tritium unit) = 1 atom of H-3 per 1018 atoms of H-11TU = 7.19 dpm/L = 0.118 Bq/L= 3.19 pCi/L of H2O
Natural activity in precipitation – about 25TU at high altitudes, about 4TU in the equatorial zone
Michael F.L’Annunziata “Handbook of ….
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C-14
• Emax= 156.48 keV• T1/2 = 5700 y• pMC - percent modern carbon, proportion of C-
14 activity in the sample compared to the C-14 standard activity.
• Standard activity - define as 74.59% of activity of oxalic acid SRM 4990C.
• 100 pMC = 13.56 dpm/g = 0.226Bq/g=6.108 pCi/g C
Michael F.L’Annunziata “Handbook of ….
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Liquid Scintillation
T. DeVol et al
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Scintillation
• Flash of light with 375-430 nm wavelength range
• Beta pulse decay time – 2-10 ns• Alpha pulse decay time – 40-50 ns• The intensity of light flashes is directly
proportional to the original nuclear decay energy dissipated in the cocktail
• 10 photons per 1 keV energy absorbed in LSV
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LS Analysis
• LS Counter• Vials• Cocktails• Sampling• Sample preparation for counting• Counting• Data evaluation
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LS Counters
• LSC should be able to:– Detect light flushes from LS vial– Determined number of light flushes and
their intensity– Process automatically different type of
samples
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LS Counters
Schematic diagram of modern LSC (TriCarb)Michael F.L’Annunziata “Handbook of ….
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300 SL - Hidex
Michael F.L’Annunziata “Handbook of ….
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Schematic diagram of TDCR LSA
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Triathler -Hidex
Michael F.L’Annunziata “Handbook of ….
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Vials• Glass vials- low potassium borosilicate
glass– Provide advantage of transparency for
cocktail • Plastic vials – polyethylene vials
– Unbreakable, less expensive, lower background than glass vials
– Permeable to benzene, toluene and xylenebased cocktails
– Resistant to diffusion with environmentally friendly cocktails(Ultima Gold, Opti-Fluor etc.)
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Nahle O. et al. light trapping in glass vials Vials1-plastic vial, 2- glass vial with scotch tape, 3-glass vial
1 2 3
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Nahle O. et al Vials
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Performance Vials
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LS Cocktails
• Cocktail is a media that holds sample during the analysis process– Emulsifying or aqueous cocktails (Safer)
• Organic aromatic solvent• Scintillator• Emulsifier
– Organic or non-aqueous cocktails (Classical)
• Organic aromatic solvent• Scintillator
Michael F.L’Annunziata “Handbook….
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LS Cocktails-Solvents
T.DeVol et al.….
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LS Cocktails-Scintillators
• Scintillators– 2,5-diphenyoxazole (PPO) and– p-bis-(methylstyryl)benzene (bis-MSB)
is the most popular combination
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LS Cocktails-Surfactants• Surfactants form micro emulsion “oil-in-
water” (~ 10nm droplet size) to ensure energy transfer:– Nonionic – alkyl phenol ethoxylates are the
most popular surfactants found in most cocktails
– Anionic – Cationic– Amphoteric
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LS Cocktails-Evaluation
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Michael F.L’Annunziata “Handbook of ….
LS Cocktails for H-3
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LS Cocktails for C-14
• CarboSorb E, Optisorb-1(PE), Carbo-Trap (Baker), Carbomax Plus (Lumac), Carbomate-2 (N.D.), Zintol-II (Zinsser)– CO2 + amine → carbamate
• Permafluor E, Optisorb S(PE),14C-Fluor (Baker), Oxosol-306(N.D.), Zintol-X(Zinsser)
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LS Cocktails for C-14
Michael F.L’Annunziata “Handbook of ….
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LS Cocktails
• Aupiasis J. et al.– Elaborated discussion on energy transfer
within the cocktail
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Counting interferences factors
• Quench• Background• Luminescence• Static electricity• Wall effect
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Quench in LSC• A reduction of the light reaching the
photomultiplier tube• Quench alters the light production and
transmission process. • IT DOES NOT ALTER THE ENERGY OF
THE PARTICLE.• Types of Quench
– Self Absorption– Color (Optical)– Chemical
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Quench in LSC• Self-absorption quench occurs when radiation
emitted from a sample remains undetected due to entrapment in a non-scintillating media
T.DeVol et al. ….
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Quench in LSC• Chemical quench–interference with
production of photons in the scintillator(compounds scavenge the excitation energy from the solvent, interfere with energy transfer from solvent to solute)
• Chemical quench is loss of energy
T. DeVol et al ….
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Quench in LSC• Color quench is the result of absorption of the
scintillation photons before they are detected by the photomultiplier tube
• Color quench is the loss of light
T. DeVol et al…
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Quench in LSC
Michael F.L’Annunziata “Handbook of ….
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Michael F.L’Annunziata “Handbook of ….
Quench in LSC
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Quench in LSC
Michael F.L’Annunziata “Handbook of ….
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Quench in LSC
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Quench correction
• Internal Standard Method
• Sample spectrum characterization methods
• Direct DPM methods
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Quench correction-Internal Standard
• Internal Standard MethodE=(Cs+i-Cs)/Ai
As= Cs/E– Cs – count rate of sample– Cs+i – count rate of sample after addition of
internal standard– As, Ai – activity of sample and internal
standard– E – counting efficiency
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Quench correction – Spectrum characterization
• Sample spectrum characterization methods
– H# - Beckman– SQP – Wallac, Hidex– G# -– SIS- PE– tSIE-PE
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Quench correction – Direct DPM counting
• Direct DPM methods– Efficiency tracing with C-14– Triple-to-double coincidence ratio (TDCR– NIST/CIEMAT efficiency tracing
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Quenching correction -Color
• Color quench:– Decolorized (bleaching or oxidation)– Use color correction software of the
instrument– Count separate set of standards for color
quenching correction
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Quenching effects
• Komosa A, Slepecka K.
– 9 commercial cocktails, two type of vials – low potassium glass vial and low diffusion Teflon coated PE vial
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Komosa A, and Slepecka K. Quenching Effects..
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Background
• Counts from sources external to the sample1.Instrument -10%2. Crosstalk - 22%3. Vial and PMT face - 37%4. Scintillator - 31%
Michael Kessler ….
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Michael Kessler ….
Background
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Background
• Background count rates are determined by counting a blank samples
• The majority of background counts are found in 0-5 keV energy range
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Background
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Michael F.L’Annunziata “Handbook of ….
Background Reduction, Vial material and size
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Background Reduction - Region optimization
Michael F.L’Annunziata “Handbook of
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K-40 contribution, Gonen R.et al.4.27 0.98% in H-3 spectrum
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Background Reduction
• Temperature control– Cooling used to minimize thermal noise from
PMT. In contemporary LS counters cooling optimizes sample chemistry
• Shielding– Passive (lead)– Active ( BGO guard detector)
• Pulse Discrimination ElectronicsMichael F.L’Annunziata “Handbook
of ….
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Background ReductionPulse Discrimination Electronics
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Background Reduction-Pulse Discrimination Electronics
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Luminescence
• Luminescence refers to emission of light photons due to energy absorption and concomitant molecular excitation from origins other than nuclear radiation. Contribute to the background through random coincidence effects in PMT that view the sample– Photoluminescence– Chemiluminescence
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Photoluminescence
• Result of the exposure of the sample to UV light
• Single photon event and decays in 10-15 minutes
• Light emitting substance can be repeatedly activated
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Chemiluminescence
• One time event when mixing cocktail and sample due to chemical reaction
• Single photon event• The majority of the counts are in 0-6
keV region• Two counting regions can be used to
detect chemiluminescence
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Chemiluminescence
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Luminescence control• Chemical methods –neutralization with
nonoxidizing acid, neutralization before adding a cocktail, use of special cocktails (Hionic-Fluor).
• Temperature control – cooling slows down the reaction, heating up to 40oC drives reaction to its endpoint.
• Counting region setting• Delayed coincidence counting
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Static
• Electrostatic discharge is photon-producing event of random nature
• Methods for reducing or eliminating static:– Electrostatic controller – Selection of vials (antistatic plastic vials)– Antistatic wipes– Humidification of sample preparation and
counting areas
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Wall effect
• Applies to plastic vials and traditional cocktails:– Cocktail penetrates plastic vial and causes
scintillation.– Quench indicating parameter would be
erroneous, providing wrong counting efficiency, and as result wrong activity of the sample
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Sampling and counting of H-3• Samples should be sealed in airtight
containers (glass or HD plastic)• When samples are exposed to outside air. It
should be assumed that contamination is possible and monitoring is required.
• Purification of water samples is recommended if (1) color is visible, (2) organics are present or (3) sample history is unknown
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Sampling and counting of H-3
• Sample purification/Extraction techniques
– Filtering– Ion exchange– Freeze drying– Azeotropic distillation– Distillation
Michael F L’Annunziata “Handbook of
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Sampling and counting of H-3
• Madruga M.J et al. Determination of H-3 in waters – Distillation and Electrolytic enrichment– 8/12 UG LLT – 20 ml glass vial
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Sampling and counting of H-3• Z.Tosheva et al.
– Comparison of Distillation (ISO- 9698) and chromatographic (Eichrom OTWO2) methods for H-3 determination:
• 250 ml sample for distillation – up to 7 hours• 25 ml sample for chromatography – 30 min
– Comparison of 6 cocktails:• UG LLT, UG XR, Pico Fluor LLT, OptiPhase
HiSafe 2 with added Triton X100, OptiPhaseHiSafe 3 and OptiPhase TriSafe for efficiency, background and MDA
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Sampling and counting of H-3
• Gudelis et all.– Water from the wells around Waste
Storage facility:– Water and soil– MDA - 0.8 Bq/l for 2800 min 12+8 ratio– H-3 range up to 105 Bq/l
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Sampling and counting of H-3
• Pujol L. et all.– National network– No distillation, UG LLT 10/12– MDA 1.5-2.3 Bq/L– Background – 0.8-2.6 cpm– Counting efficiency - ~ 20%– Detailed discussion of H-3 level in
“nuclear” vs “non-nuclear” rivers
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Sampling and counting of H-3
• Gonen R. et all (OBT in Urine)– Biological half-life of OBT is 4 times greater than
for HTO– OBT determination is time consuming– Direct determination:– (HTO+OBT)- from analysis of total urine,
2ml urine+14ml UG XR+ 4 ml water – HTO – after filtration through charcoal, 20 ml of
urine + 3g active charcoal, 2ml of filtrate+14ml UG XR+4ml water
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Gonen R. et all (OBT in Urine)• Chemi- and photoluminescence are
discussed, chemiluminescence'sspectrum overlaps both H-3 and C-14 spectra
• K-40 contribution is considered• ANSI-N13.30 HPS 1996 –
recommendations• MDA for 45 min counting –
0.058Bq/sample (Quantulus 1220)
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Baglan N. et al, OBT round-robin exercise
• 11 laboratories were participating in CETAMA (Comite d’ETAblissement des Methodes d’Analyse) organized round-robin exercise
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Sampling of C-14
• Benzene synthesis– Most accurate, used in dating
• Direct counting– limited application
• CO2 Absorption• Sample preparation is less time-consuming• Limited amount of carbon can be absorbed (0.7g
vs 10g for benzene)
Michael F.L’Annunziata “Handbook of ….
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Sampling and Counting of C-14
Molnar et al
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Sampling and Counting of C-14
Michael F.L’Annunziata “Handbook of ….
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Svetlik I et al., C14O2 in grab samples
• Samples were collected in high pressure (200 atm) SS bombs – 30 min, 150-350L
• Samples were stored for 1 month to reduce background from short-lived radionuclides
• Samples were transferred to low pressure gas bags with 2 outlets
• Gas was pumped from the gas bag through gas meter to series of traps (washing - 1% H3PO4, absorbing – 3M NaOH and condensation trap – 1% H3PO4 ) and back to the gas bag.
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Svetlik I et al., C14O2 in grab samples• 1 sorption cycle – 33-36% of CO2• 13 cycles – above 98%• Finally system was purged with N2• 8g out of total ~ 50g of Na2C14O3 were used to
prepare duplicate final samples 5 g each with pH~9.3 Diluted H2SO4 was used to adjust the pH
• 15 ml of Hionic-Fluor (PE) were added• Counting efficiency – 32-34%• Background – 6.5 cpm• Counting time – 60 min • For the total combustible C-14 – CuO catalyst (at
700oC) was inserted between gas bag and gas meter
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Svetlik I et al., C14O2 in grab samples
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Varlam C. et al.Optimization of C-14 measurementFaurescu I. et al. C-14 in Danube River
• Precipitation of dissolved inorganic carbon as carbonate
• Acidification and release of CO2
• Direct absorption of CO2 in tertiary amine
• Addition of scintillation solution and counting
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Saxen R.and Hanste U.M, C-14 in foodstuff
• Automatic oxidizer Model 307 (PE)• CO2 is absorbed by CarboSorb E• Permafluor E cocktail added to the
sample• 2000-2007 ~ 125 Bq/kg C in mixed diet• Annual dose ~ 10μSv/yr (12 μSv/yr –
“natural level”)• No increase due to discharge from
NPPs
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C-14 Vartii V-P, Optimizing counting
• CarboSorb is a strong quenching agent, background sample should be adjusted to match the same quench as in the sample
• 10 ml of CarboSorb can take up 48 mmolesof C, that limits sample size to 1g
• It very challenging to prepare representative sample
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Molnar et al., Refining the CO2 absorption …
• Carbosorb (PE) – 11 ml, Mean absorbed amount of CO2 – 1.98g (82% saturation), 0.54g of C
• Permafluor E (PE) – 11 ml • Counting time – 1020 min• TriCarb 3170, 7-52 channels, FM=2283
FM=E2/B, Bkg. 1.869 .020 cpm
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C-14 Vartii V-P, Optimizing counting
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Do-Sung Kim et al . Retrieval estimation of gaseous C-14 discharged..
• CANDU – PHWR 700MWe x 4• Retrieval of discharge rates for H-3 and C-14 from
pine trees rings• Rings were separated, ground and dried. α-Cellulose
was extracted, dried and burned• Water was used for OBT determination• CO2 was absorbed by NH4OH and precipitated as
CaCO3
• Nitric acid was added and CO2 trapped in LS vial• Samples were counted for 600 min (30 min x 20)
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Do-Sung Kim et al . Retrieval estimation of gaseous C-14 discharged..
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Do-Sung Kim et al . Retrieval estimation of gaseous C-14 discharged..
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Do-Sung Kim et al . Retrieval estimation of gaseous C-14 discharged..
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Noakes J. et al.,A comparison of analytical …
• ASTM D 6866-05 for USDA Biobasedproducts:
– Accelerator mass-spectrometry (AMS)– Benzene synthesis– LSC of CO2
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Noakes J. et al.,A comparison of analytical …
– 20 ml vial, 10 ml Carbosorb E, 10 ml Permafluor
– 10 ml Carbosorb E – 1L CO2 at STP– Amount of CO2 determined by weight– Linearity of absorption is verified– 1l CO2– 0.45 g C
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Noakes J. et al.,A comparison of analytical …
– 56-66% efficiency– Background – 2.53 - 4.08 dpm/g– Preparation time –3 h– Analysis time – 1300 m– Analysis cost - $250– Instrument cost – $100,000
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Culp R. et al., Further development of ASTM 6866-06
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Resources
• Michael F.L’Annunziata– “Handbook of Radioactivity
Analysis”, Academic Press 2003• Michael J. Kessler,
– Liquid scintillation analysis, Science and Technology, Publ.No.169-3052, Packard Instrument Co.
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Resources
• Series of “Advance in Liquid Scintillation Spectrometry”, Radiocarbon, The Univ.of Arizona, Tucson, Arizona, USA.
• ISO –9698 - distillation method for H-3• Eichrom H-3 column method
(Ref.#OTWO2)
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Resources
• www.lsc-international.org
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Reference - vials
• Nahle O. et al, Study of light emission processes for the design of LS counters, LSC 2008, Advance in Liquid Scintillation Spectrometry, pp87-95
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Reference - cocktails
• Komosa A., Slepecka K., Study of quenching effects for C-14 and H-3 measurement parameters using a Quantulus spectrometer, LSC 2008, Advance in Liquid Scintillation Spectrometry, pp161-172
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Reference - H-3• 1. Gonen R. et all., Background contribution in LSC for
determination of OBT in urine samples, LSC 2005, Advance in Liquid Scintillation Spectrometry, p359-368
• 2 Gudelis A. et all.,Results of tritium monitoring in the environment of the Maisiagala Radioactive Waste Depository, LSC 2005, Advance in Liquid Scintillation Spectrometry, p331-341
• 3 Pujol L. et all, Overview of the Environmental Monitoring Program for H-3, LSC 2005, Advance in Liquid Scintillation Spectrometry, p369-381
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Reference H-34. Aupiasis J. et all. Variation of counting efficiency of H-3
in LSC cocktails with different components and evaluation of theoretical calculation of time transfer of cocktails, LSC 2005, Advance in Liquid Scintillation Spectrometry, p383-394
5. Z.Tosheva et al. Easy and Rapid estimation of ofenvironmental H-3 with Eichrom column and LSC measurement, 2005, Advance in Liquid Scintillation Spectrometry, p383-394
6. Baglan N. et al. Assesment and interpritation of a round-robin exercise for OBT determination, 2008, Advance in Liquid Scintillation Spectrometry, p229-240
6
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Reference C-14• 1. John Noaks et al., A comparison of analytical
methods for the certification of biobased products, LSC 2005, Advance in Liquid Scintillation Spectrometry, p259-271
• 2. Do-Sung Kim et al. Retrieval estimation of gaseous C-14 discharged rate using C-14 and H-3 concentrations in pine tree rings in the vicinity of Wolsung NNP, LSC 2005, Advance in Liquid Scintillation Spectrometry, p401-406
• 3. Molnar et al., Refining the CO2 absorption method for low-level C-14 LSC in the ATOMKI, LSC 2005, Advance in Liquid Scintillation Spectrometry, p407-416
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Reference C-14
• 4. Svetlik I et al., Determination of CO2 in grab samples of stackair from NPPs., LSC 2005, Advance in Liquid Scintillation Spectrometry, p417-422
• 5. Do-Sung Kim et al. Retrieval estimation of gaseous C-14 discharged rate using C-14 and H-3 concentrations in pine tree rings in the vicinity of Wolsung NNP, LSC 2005, Advance in Liquid Scintillation Spectrometry, p401-406
• 6. Molnar et al., Refining the CO2 absorption method for low-level C-14 LSC in the ATOMKI, LSC 2005, Advance in Liquid Scintillation Spectrometry, p407-416
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Reference C-14
• 7. Varlam C et al.,, Optimization of C-14 measurement in aqueous samples using the direct absorption method and LSC, LSC 2005 Advance in Liquid Scintillation Spectrometry, p423-428
• 8. Saxen R and Hanste U.M, An oxidizer/LSC method for the determination of C-14 in foodstuff samples, LSC 2008 Advance in Liquid Scintillation Spectrometry, p279-285
• 9. Faurescu I. et al., Radiocarbon measurements in Romanian Danube river water, LSC 2008 Advance in Liquid Scintillation Spectrometry, p339-344
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Reference C-14
• 10. Vartii Vesa-Pekka, Optimizing the counting conditions for C-14 for the sample oxidizer-liquid scintillation counter method, LSC 2008 Advance in Liquid Scintillation Spectrometry, p293-298
• 11. Culp R. and J. Noaks, Evaluation of biobasedcontent ASTM 6866-06A:impruvments….., , LSC 2008 Advance in Liquid Scintillation Spectrometry, p269-278